Re: [PATCH 01/15] perf_counter: unify and fix delayed counter wakeup

[Paul Mackerras]

Peter Zijlstra writes:

> +void perf_counter_wakeup(struct perf_counter *counter)
> +{
> +	struct perf_mmap_data *data;
> +
> +	rcu_read_lock();
> +	data = rcu_dereference(counter->data);
> +	if (data) {
> +		(void)atomic_xchg(&data->wakeup, POLL_IN);

Really just a nit, but how is this atomic_xchg any different from
atomic_set(&data->wakeup, POLL_IN) aside from being slower?

Paul.
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